Damage to articular cartilage results in significant disability to many people, young and old alike. Damaged articular cartilage has very limited capacity to repair itself and restore normal function. The repair tissue that is formed in response to damaged articular cartilage is often in the form of fibrocartilage, which does not have the load-bearing capacity of the original articular cartilage. Also fibrocartilage does not exhibit the lubricating ability as does hyaline or articular cartilage. Over time this leads to further destruction of the cartilage and eventually to osteoarthritis. For older patients, one solution to this problem is total joint replacement. However, for younger patients who suffer from cartilage defects and lesions, another form of treatment is needed.
Reconstructive orthopaedic surgery is becoming increasingly necessary to treat patients with damaged cartilage deriving from congenital abnormalities or trauma. Current therapies include transplantation or allografts, implantation of artificial prosthetic devices, and neo-cartilage formation utilizing isolated chondrocytes in an organic support matrix or scaffold. However, each of those methods for repairing damaged cartilage has associated risks. In addition to complications by infection and host versus graft rejection, there is a high incidence of incomplete or disrupted bonding at the host-implant interface. Problems with adhesive bonding are particularly predominant, for example, at articular cartilage joints where the bonded surfaces are continuously bathed in synovial fluid. Hydration/lubrication of cartilage surfaces by synovial fluid is one of the major causes of problems associated with adhesive bonding to such surfaces
A variety of adhesives or surgical glues has been studied for repair of cartilage and other tissue surfaces. Bioerodable adhesives may include fibrin-based materials, poly(amino acids), and designed polypeptides.
When the implant includes a polymer matrix, the polymer matrix can be glued to damaged cartilage to provide a bonded porous three-dimensional scaffold that can serve as a support for bioactive materials and for growth of chondrocyte cell populations. The scaffold serves as a template to help define the shape of the new tissue as it is being regenerated. If the synthetic material is a bioerodable or biodegradable polymer, the scaffold gradually degrades into natural metabolites which are removed from the defect site. Optimally, the repair tissue strongly resembles and functions as that of native cartilage.
The success of such treatment for repair of damaged cartilage depends in part on the ability of the surgical glue to bond to and stabilize the implant, transplant or polymer scaffold to the defect site. One characteristic of normal articular surfaces is its hydrophobicity. The hydrophobic cartilage surface comprises a phospholipid layer that provides lubricity for articulating cartilage surfaces in a normal joint. Unfortunately the same hydrophobic character of the articular surfaces which provides the low-friction interface also reduces the effectiveness of surgical glues to form a strong bond between native cartilage and implanted repair material. Hydrophobic components on the surface interfere with the adhesion of surgical glues to the cartilage surface, and it has been found that they are difficult to remove from the cartilage surface to improve surface bonding.
In addition to the hydrophobic character of cartilage surfaces, the synovial fluid which continuously bathes joint tissues also interferes with the bonding of joint tissues using conventional surgical adhesives/glues. In vivo synovial fluid continuously wets the surfaces of articular joints and the associated cartilage, tendon and ligament surfaces. Synovial fluid appears to have two main functions: the lubrication and nutrition of the joint tissues. Synovial fluid is comprised of a complex mixture of macromolecular constituents including components derived from the blood, substances secreted by the joint tissues, and products derived from catabolism of the joint. One of the main constituents of synovial fluid is hyaluronic acid. Hyaluronic acid is a polyacidic polysaccharide. In the joint surfaces, hyaluronic acid is believed to interact with proteoglycans to form large aggregates collectively providing a homogeneous matrix on articular cartilage surfaces. In the proteoglycan matrix, hyaluronic acid is covalently bound to polypeptides comprising keratin sulfate and chondroitin sulfate chains via smaller linker proteins. The proteoglycan matrix can be repeatedly compressed and still return to its original shape after being deformed. The matrix helps cushion the compressive forces on articular cartilage surfaces.
The biological components existing in vivo on cartilage surfaces and in articular joints work to prevent or diminish the effectiveness of surgical glues to bind and stabilize transplants of native cartilage or implants of synthetic material to cartilage surfaces in need of repair. There is need to improve the effectiveness of surgical glues to bond cartilage surfaces in connection with surgical reconstruction or repair of joint structures
One embodiment of the present invention addresses that need. It is based in part on the discovery that cartilage surfaces wet with synovial fluid can be treated with a composition comprising a poly(hydroxy substituted amino acid) to enhance the bonding of the cartilage surface with surgical adhesives/glues. It has been found that synovial fluid forms a liquid crystalline composition when combined with poly(hydroxy substituted amino acids). The synovial fluid appears to exhibit a greater affinity for the added polypeptide than for cartilage components, thus resulting in modification of the cartilage surface characteristics. Complexing the synovial fluid associated with the cartilage surface to form the gelatinous liquid crystalline matrix increases the effectiveness of glue or cement to bind the cartilage surface. Optionally the gelled matrix can be separated from the cartilage, prior to application of the surgical glue to further improve bonding of the surface with surgical glues.
Thus, one aspect the present invention relates to a novel liquid crystalline composition comprising a poly(hydroxy substituted amino acid) and synovial fluid.
Another aspect of this invention relates to an improved method of preparing a cartilage surface to enhance the efficacy of surgical glues to bind to the cartilage surface.
Yet another aspect of this invention is an improved method of removing synovial fluid from cartilage surfaces and articular cartilage joints by contacting the cartilage surface (wetted with synovial fluid) with a poly(hydroxy substituted amino acid) to form a liquid crystalline matrix that can be readily removed from the cartilage surface.
In another embodiment of the invention, there is provided a more general method of modifying the surface characteristics of tissue in vivo by forming a liquid crystalline or mesomorphic matrix on said surface wherein the matrix comprises a component of the tissue surface or a component of a fluid wetting the tissue surface. The matrix can optionally be removed to provide a surface having a reduced amount of said component.